1. Field of the Invention
This invention relates to a method of manufacturing magnetic head air bearing sliders, and more particularly to a method for fabricating structural elements in magnetic head air bearing sliders using an etching process.
2. Description of Related Art
Magnetic recording systems utilizing transducers that are supported by an air bearing layer as they move relative to the surface of a magnetic recording disk are well known in the art. Such transducers "fly" on a layer of pressurized air at just a few microinches above a rotating disk surface. The transducer is mounted in a slider assembly which has a contoured surface. The air bearing layer is produced by pressurization of the air as it flows between the disk and slider, and is a consequence of the slider contour and relative motion of the two surfaces. The purpose of the air bearing is to provide, with minimal or no contact, a very narrow clearance between the slider and rotating disk. This allows a high density of magnetic data to be transferred and reduces wear and damage to the magnetic assembly and recording media during operation.
Typical sliders of the prior art, as illustrated in FIG. 1, utilize at least two lower rails 1a, 1b having flat surfaces 2 oriented toward the recording medium. Each of these rails 1a, 1b has a tapered forward surface 3a, 3b oriented against the direction of rotation 4 of the recording medium. The rotating recording medium forces air by viscous effects into the tapered forward surfaces 3a, 3b and thereby produces a pressure beneath each of the rails 1a, 1b, resulting in the air bearing. These sliders are typically gimbal-mounted to a flexure which is attached to an arm. The arm is driven by an actuator which positions the transducer over the recording surface from one data track to another. The arm can move in a linear motion (which is termed linear access) or it can rotate about a pivot point (which is termed rotary access). With rotary access, the slider will be positioned at varying angles with respect to the direction of disk rotation as the slider moves over the recording surface. This angular orientation is referred to as the "skew" angle.
When a typical slider is positioned so as to have any angular skew, the rotation of the recording medium introduces pressurized air at the forward edge of the slider, thereby generating the air bearing. However, this air is pressurized at a reduced value because of the skew, thus giving rise to a reduction in the flying height. Also, the skew angle gives rise to a roll of the slider such that the air bearing flying height is not uniform under both of the rails 1a, 1b. Accordingly, the position of the transducer with respect to the recording medium can vary as the slider is caused to roll in one direction or the other or fly at different heights. Such variations in flying height adversely affect the data transfer between transducer and recording medium. In particular, the density of bit storage is adversely affected if the flying height of a slider is increased.
Furthermore, the slider must move radially across the recording medium at a substantial rate of speed to access various portions of the medium. This motion also introduces air under one edge of each slider rail 1a, 1b and results in a roll of the slider and a change in the spacing between the transducer and the recording medium. When any of these variations of spacing occur, particularly with a substantially reduced spacing between the slider and the recording medium, contact may occur between the slider (and its transducer) and the recording medium, or at least potentially rough surfaces thereof. Any such contact introduces wear into the slider and the recording surface.
Moreover, the relative speed between the magnetic disk and the slider varies as a slider moves from an inner diameter of the recording medium to an outer diameter. Such variations in speed result in variations of air flow under a slider, which changes the flying height of the slider. As noted previously, such variations in flying height adversely affect the data transfer between transducer and recording medium.
One solution that has been proposed for minimizing change in the flying height and roll of a slider as skew angle or relative air flow speed changes is to provide a transverse pressurization contour along each side edge of the air bearing surfaces 2 of the slider such that any air flow from the side of the slider assembly due to skew angle and/or access velocity produces pressurization adjacent to one side edge and depressurization (or expansion) adjacent to the other side edge of each air bearing surface 2. Such a transverse pressurization contour (or "TPC") causes a pressure distribution across each air bearing surface 2 that is substantially symmetrical from side to side. This construction makes the slider assembly flying height and roll angle essentially insensitive to skew angle and/or access velocity and/or air flow speed. A design of a slider having such a transverse pressurization contour is disclosed in U.S. Pat. No. 4,673,996. That patent shows three transverse pressurization contours for air bearing sliders (see FIGS. 6 and 7 of that patent).
One problem that arises with the TPC design is in fabricating the fairly precise angles or angular structures required to form the transverse pressurization contour on an error bearing edge. Considering the contours shown in U.S. Pat. No. 4,673,996, the angled contours of the left hand air bearing surface of FIG. 6, and the rounded contours shown in FIG. 7, are difficult to manufacture on a repetitive, reliable basis. The "stepped" TPC structure shown in the right hand air bearing surface in FIG. 6 is generally more desirable from a manufacturing point of view because the width and depth of the step structure can be more readily controlled than an angled or rounded contour. Moreover, in terms of the horizontal lift surface provided for the slider air bearing surface, the step structure is preferred.
Even though the step structure is preferred over the other transverse pressurization contours, such a structure is still quite expensive to manufacture. Normally, such a step structure could not be machined into the slider air bearing surface using conventional machining. The depth of the step is typically about 30 microinches, .+-.5 microinches. Conventional machining in a production environment permits tolerances of only about .+-.300 microinches. Further, since the entire width of a typical air bearing surface is only about 0.635 mm, and the typical width of each TPC is about 127 mm (meaning that about 40% of the air bearing surface of a rail is occupied by two TPC's for that rail), such machining is difficult and time consuming, and therefore expensive.
A second method of fabricating such a step structure would be to etch (e.g., chemically etching) the slider material. However, most sliders are made of calcium titanate or polycrystalline ferrite material, zirconia, or alumina titanium carbide (for thin film heads). These materials are not generally etchable with the degree of precision required to make a step structure. While single-crystal ferrite material can be chemically etched, this material is at present quite expensive, and requires a relatively expensive photomasking operation to shield portions that are not to be etched.
Another method for forming the TPC step structure is ion milling. However, this process is expensive.
Therefore, it would be desirable to have a method of forming transverse pressurization contours into the air bearing surfaces of a slider at low cost, and with the precision requisite in forming such TPC's. The present invention provides such a method.